1. Field of the Invention
This invention pertains generally to the generation of nano-scale patterning on suitable surfaces and particularly to force directed nanoparticles utilized in nanopatterning, by inducible reactions, the surface of self-assembled monolayers that are anchored to atomically smooth surfaces. More particularly to electrophoretically directible photocatalytic quantum dots employed in nanopatterning, by photochemical reactions, the photocatalytically active surface of self-assembled monolayers that are anchored to atomically smooth surfaces. For exemplary purposes only and not by way of limitation, the stages involved in an embodiment of the subject nanopatterning comprise preparing and characterizing atomically smooth surfaces, synthesizing azide functionalized self-assembled monolayer (SAM) and modifying the smooth surface, synthesizing CdS and/or CdSe quantum dots of various sizes, characterizing and adsorbing them onto the SAM surface, photocatalytic reduction of the azide functionalized SAM and characterizing the reduced surface (using FTIR, STM, etc.), and demonstrating electrophoretic mobility of the quantum dots on the SAM with the simultaneous photocatalytic reduction to obtain nanopatterns.
2. Description of Related Art
Standard lithographic techniques for producing markings on surfaces will reach their useful limit for complex surface patterning at a feature size of ˜100 nm. If the predicted size, speed and power advantages of molecular electronics are to be realized completely, means must be achieved to create complex patterns with a feature size of ˜5-10 Å. At this molecular limit, logic devices with densities on the order of 1012 gates/cm2 become conceivable.
Several researcher groups are working to develop nanocircuitry based on the self-assembly of carbon nanotubes into a two-dimensional grid. Others, (see below) plan to etch surface patterns using arrays of scanning probe microscopy (i.e., AFM or STM) tips. Both of these approaches are fundamentally different than the subject invention and do not permit the simultaneous creation of a billion or more (virtually an unlimited number) copies of a complex, user-defined nanopattern at high density on a surface.
Specifically, impressive progress has been made toward realization of nanoscale, molecular electronic devices. (1-3) Plausible designs have been conceived (3) and exciting experimental progress has been achieved. (4, 5) For example, Heath et al. (4) describe a molecular-based logic gate where redox-active rotaxanes serve as the switching elements. Rotaxanes are multicomponent structures consisting of a large dumbbell-shaped molecule and one or more ring-shaped molecules trapped on the dumbbell. The rotaxane used in this study showed 60- to 80-fold change in conductivity with redox state. Thus, this “molecular switch” could be opened by oxidizing the molecule resulting in dramatically reduced current flow. Although these rotaxane-based switches open irreversibly, Heath et al. envision such molecular switches as constituents of a chemically assembled electronic nanocomputer (CAEN), which will be based on chemically synthesized and assembled nano- or molecular-scale components including molecular-scale wires.
Given the finite yields of chemical reactions, a CAEN would have many defects. In an earlier publication, Heath et al. demonstrated a concept for a highly defect tolerant computer architecture that is directly relevant to CAEN design. (6) Their experimental system was a massively parallel computer built of relatively inexpensive components containing many defects. In their design, a “tutor” system locates and tags CAEN defects, which subsequently can be circumvented thereby enabling surprisingly powerful computational performance. However, an approach to assembling an actual CAEN with the necessary interconnections between molecular- or nano-scale logic gates has not been demonstrated in the laboratory.
Most proposed approaches to patterning surfaces at the molecular scale rely on AFM or STM, or self-assembly, although recently, “nanolithography at the Heisenberg limit” was reported which gave pattern resolution of ˜20 nm. (7) This process did not involve lithography in the usual sense, rather a beam of metastable argon atoms passing through an optical standing wave was de-excited with a spatial dependence that resulted in the patterning of silicon or silicon dioxide substrates in the atom-beam path. A simple pattern of lines was created with a feature size limited by the Heisenberg uncertainty principle as applied to the position and momentum spreads of the localized metastable atoms. Although impressive, it is not apparent how this technique could provide a route to generation of complex, user-defined nanopatterns.
Ten years ago, researchers demonstrated the use of STM to deposit Xe atoms in precise locations to spell “IBM” on a single-crystal Ni substrate. (8) This impressive feat led to widespread speculation that scanning probe microscopy could lead to viable approaches for the nanopatterning of surfaces. More recently, another group showed that when silver nanoparticles are nudged along a silicon surface with an STM tip they leave behind a track of silver atoms. (9) In this way, “nanowires” might be drawn on a surface. However, as with the earlier STM work, huge technical obstacles remain in the development of STM-based nanopatterning of surfaces of the kind needed for nanocomputers where a repetitive pattern must be created over a macroscopic surface area. Patterning a macroscopic surface with a single STM tip would be impracticably slow, and processes based on vast arrays of tips appear enormously complex and expensive.
Many believe that the self-assembly approach will provide a means to generate molecular-scale patterns useful for nanoelectronic device manufacture. Indeed, many examples of highly ordered surface nanopatterns have been published based on molecular self-assembly of block copolymers and surfactants, for example. (10) The science of self-assembly still is in its infancy, however, and it is not a straightforward matter to program molecules to assemble into an arbitrary, user-defined nanopattern that would give the necessary interconnections between sites for logic gates.